Background: Colorectal leiomyosarcoma (LMS) is a rare colorectal malignancy accounting for approximately 1% of all colorectal malignancies with a poor prognosis and limited treatment options. Targeted therapies have been applied for breast cancer 2 (BRCA2) alterations, but their role remains to be explored in colorectal LMS. This case could provide clinical proof for the application of olaparib for LMS patients. Case Description: Here, we present a case of colorectal LMS with BRCA2 alterations who was treated with olaparib and achieved progression-free survival (PFS) for 1 year. In August 2016, a 46-year-old female patient was admitted to hospital due to a mass in the left lower abdomen and was diagnosed with LMS of the sigmoid colon. After surgical resection, chemotherapy with ifosfamide or ifosfamide combined with pirarubicin was given and achieved stable disease (SD) until the disease progressed 1.5 years later. Afterwards, a multi-target tyrosine kinase inhibitor, anlotinib, was taken. Before the observation of lung and liver metastasis, the patient's disease was stable for 1 year. BRCA2 mutation and rearrangement was revealed by next-generation sequencing (NGS), and the targeted therapy, olaparib, was given. Efficacy evaluation showed SD for 1 year, and no obvious toxic and side effects were observed. Conclusions: Our case suggested that NGS should be considered for further treatment of patients with colorectal LMS, and poly (ADP-ribose) polymerase (PARP) inhibitors could be a feasible therapy for LMS patients with BRCA2 alterations.